This invention relates to cryogenic freezers, and in particular to a trap or seal system for preventing undesired air infiltration into a freezer.
Cryogenic freezers for freezing of food products can be of many forms. For example, U.S. Pat. No. 4,783,972 illustrates a tunnel-type freezer while U.S. Pat. No. 4,878,362 illustrates a spiral-type freezer. In any type of freezer, for freezing purposes, a cryogen, such as liquid nitrogen or carbon dioxide, is employed for quick and effective freezing of food products.
A substantial and costly problem facing cryogenic freezers has always been infiltration of moisture-laden air. Air infiltration can also pose problems in mechanical type freezers. In the inventor's experience, cooling of the air and freezing of moisture from the air in a cryogenic freezer can account for consumption of the freezing cryogen of as much as 700 pounds per hour. As a result, freezer manufacturers have attempted to limit the infiltration of air into a cryogenic freezer by installing computer-controlled balancing of gas flow within the freezer, plastic flaps at the entrance, and other expensive and less than fully effective controls.
U.S. Pat. No. 2,059,970 discloses an immersion-type cryogenic freezer which attempts to trap and reuse gaseous cryogen which boils off the volatile refrigerating liquid used. While a raised trap is provided at the entrance and exit ends of the freezer, no positive seal is provided to prevent air infiltration.
U.S. Pat. No. 2,787,141 discloses an apparatus for precooling produce, the apparatus having a conveyor belt system which includes water seals at the entrance and exit ends. For an air seal at the entrance and exit, the conveyor belt dips beneath the legs of a U-shaped vacuum chamber. Produce is conveyed upwardly through a first leg of the U where it is conveyed to a cooling vacuum chamber, and then through the second leg of the U for downstream handling. The apparatus would not be satisfactory for freezing, however, since water is used as a seal, and freezing in a vacuum chamber is costly and ineffective.